Nearly $6.5bn was wiped off Twitter’s value in extended trading on Wednesday night, after the social media company’s first set of results as a listed company showed a dramatic slowdown in user growth.

The San Francisco-based company's balance sheet was healthier than analysts had predicted, but investors were shaken by signs that its popularity could be starting to plateau.

The number of people who use the social network at least once a month grew 30pc to 241m in December. However, that marked a slowdown on the 39pc year-on-year increase the previous year.

The company’s revenues more than doubled from $317m to $655m last year, accelerating faster than expected in the final quarter to $243m, up 116pc. Meanwhile, the company's full-year losses widened from $79.4m to $645.3m, including a $511.5m loss in the final three months of 2013.

Investors in the social network were expected to put up with Twitter making a loss as long as it could demonstrate it was making headway in terms of revenues and users. “They understand that there is going to be an investment phase,” Ken Sena, a senior analyst at Evercore told The Telegraph ahead of the results.

However, the apparent slowdown in attracting new users sparked concerns among investors and analysts, many of whom had already warned that Twitter was overvalued when it floated for $14.2bn last November. Those fears have only grown in the following months, as the company’s value has more than doubled to $36.63bn at the close of trading on Tuesday.

“It’s at a ridiculous premium,” said James Gellert, chief executive of Rapid Ratings, told Bloomberg. “The momentum of the stock isn’t based on the current fundamentals of the company. It’s based on the promise of the future business.”

Twitter's shares plunged 15pc on Wednesday night after the results were released. They fell even furtherto 17.7pc, after Twitter’s earnings call wiping $6.5bn off the company’s market capitalisation.

It was a bruising introduction to life at the helm of a public company for Dick Costolo, chief executive.

He said the company had relied on “viral and organic” growth in the past, but that it would be “doubling down” to expand its audience in 2014.

The social network, which allows users to publish messages 140 characters at a time, will help users make the most of Twitter as a “conversational tool”, by improving the way they can search for discussions about particular topics, he said. Twitter will also make it easier for people to join, and try to get them hooked with a series of initiatives that would make it more rewarding, more quickly, for new users.

“We don’t need to change anything about the platform. We simply need to make Twitter a better Twitter,” Mr Costolo said.

He also underscored the network’s appeal to advertisers, by stressing that it was the most “democratic” of any social network, because any public message can be seen by any user.

Twitter has been relatively restrained about the number of adverts it has introduced in its feed, but it has been forging partnerships with television broadcasters so that they can offer companies joint advertising packages. The packages allow advertisers to target Twitter users who are using the social network to talk about a particular television programme.

Investors have been banking on Twitter following the same sort of trajectory as Facebook, which turned 10 years old on Tuesday and has only started making serious money relatively recently.

Last year, Facebook’s annual profits jumped to $1.5bn from $53m in 2012, after the company worked out how to make money from mobile users.